My apologies in advance for an even longer reply than yours. :-)
While I too am sad to see the tonneau case go, I see things a little differently from you.
Before I saw the latest pre-release of Da Vinci, I too was a little skeptical. In the "formal dress-watch" arena, IWC already has the Portuguese and possibly the Portofino series to fill the gap. I too was wondering how a round-case revised Da Vinci could fit into the picture.
After seeing the latest Da Vinci series in person, most of my doubts were cleared. First and foremost, the Da Vinci series were never meant to be the "ultimate high-end dress watch". OK, maybe it is--perhaps I am just misinformed. To me, the Da Vinci series have always been a technologically advanced watch that are also very elegant, not necessarily something too contemporary or shall we say post-modern? So, providing the thinnest watch by the Da Vinci series may not be the most critical aspect to consider. I mean, if "technologically advanced" is not one of the considerations, perhaps IWC could just call it the Michelangelo series instead of Da Vinci, right?
I was worried that with the Portuguese and Pilot already fully utilizing all the most advanced perpetual calendars from IWC (and Ingenieurs and Aquatimers were guilty of that too), what would be left for the Da Vinci? I was pleasantly surprised by the 89360/89361-based chronograph movements with added perpetual calendar (and moonphase) features. I hope this movement will be unique and exclusive to the Da Vinci series for a while. This sets the Da Vinci series apart--and brings back memory from the earlier Kurt Klaus designs.
Furthermore, I was told IWC spent a lot of time to get the rotating lugs right for the the new Da Vinci. None of the current IWC watches offer this. Putting this on Portofino and Portuguese will be somewhat out-of-place. Da Vinci, being the "technologically-advanced dress watch" fits in this category nicely. If you haven't seen the new lugs, all I can say is that I am thorough impressed. I would be tempted to get a new Da Vinci because of it alone.
Yes, I agree with you that putting a Sellita movement in a low-end Da Vinci does not make it too appealling... but we need to understand it is what it is... just having nice Perpetual Calendar with chronograph movements probably won't sell too many IWC's. IWC has got to have some low-end, volume products from the Da Vinci series to make some profit. My only wish is that they could perhaps consider adding a moonphase to the lower-end Da Vinci men-series, and not let that be an option for the ladies alone (after all, IWC is engineered for men, isn't it?).
All in all, I think the new Da Vinci series are full of pleasant surprises. I do love the soon-to-be-gone Tonneau case. I think IWC has done a marvelous job designing and manufacturing them. They are much more complex (and therefore costly) to make then the round case. I sincerely wish that the now-discontinued Tonneau-cased DA Vinci's will become collectors' items, and permanently a part of IWC's greatly-respected history.
If I were to worry about a particular series from IWC, it would be the Portofino rather than the new Da Vinci. The Portofino series just have so much overlapping with the Portuguese. IWC could have done much more to elevate its status. Being the only series with Roman Numerals on their dials, the Portofino could be the ultimate highest end formal dress watch for IWC, instead of the Portuguese. If you said IWC needed some ultra-thin dress watches, I think Portofino should address that market segment rather than the Da Vinci's.
I don't know... perhaps IWC could borrow more Piget or JLC thin movements and use them in the Portofino series?? perhaps that would differentiate it more from the Portuguese?
Just my 2c worth only. Feel free to disagree and add your comments.